All analogue signals produced by the detectors take a time to
process that is significant when count rates are high. Although the
anode signals only take 1 
s to process, the processing of the
wedge signals takes 3.5 s and additional time needs to be allowed
for the signal levels to settle back to zero so that in total 35 s
must elapse between successive photons. Consequently, during this
``deadtime'' the processing of any new position signals is inhibited.
At low count rates this effect is small, but it becomes more important
as the count rate increases. If the photon arrival times were
evenly spaced, then the pair of channels in one detector could see a
maximum of 
counts/sec. However, in practice the
random nature of the events, and the onset of saturation, results in a
maximum of less than half this.
In the BCS there are three sets of counters for each channel: the
total event counter, the limited (or in-window) event counter and the
encoded event counter. The gate for the limited event counter only
accepts events that fall within the allowed energy window, and in
addition inhibits any event that arrives less than 35 s after
the previous one. From a knowledge of the event counters, it is
possible to calculate the effects of the deadtime and hence
reconstruct what the count rate should be. This is done within the
MK_BSC and MKBSD routines.
It should be noted that while the event counters used for deadtime corrections are in the DP-synchronous (DP_SYNC) part the telemetry, the spectral data are in the PH stream and after passing through the queue memory are asynchronous. As a consequence, if there are holes in the data coverage, it is possible for the DP_SYNC data to be absent at the time of the spectral observations. At such times it is not possible to make a deadtime correction.